Helical micromotor operating under stationary DC electrostatic field

The direct current (DC) motor is a rotary device that converts DC electrical energy into mechanical energy. However, it is known that, in downsizing the currently available macromotor, rotary motion of DC micromotors cannot work well due to the larger viscous effect. Here, we report simple DC micromotors working under a new principle. We previously revealed that in an oil phase containing an ionic surfactant, non-spherical particles exhibit various types of regular motions such as spinning and circular orbital motions. In this study, we found that a microhelix exhibits a new type of periodic motion, namely, the cork-screw-type rotation, in a specific direction depending on the material of the helix, metal or non-metallic organics. The results show that a left-handed nickel helix rotates in the clockwise direction when viewed from the positive electrode, whereas an organic one rotates in the opposite direction (anti-clockwise) under the same electrode arrangement with stationary constant DC voltage. In addition, we demonstrate that the cork-screw rotation is switched to opposite direction by changing the handedness (chirality). It is to be noted that the micromotors reported here maintain their stable motion without any mechanical support such as rotational axes or electronic switching devices. The invented DC micromotor would be applicable for mechanical and fluidic devices, being useful as a smart device in microrobots and microfluidics.